The efficacy of the bacillus thuringiensis israelensis larvicide against culex tarsalis in municipal wastewater and water from natural wetlands

Abstract

Water quality is a factor that is likely to interact with the activity of Bacillus thuringiensis israelensis (Bti)–based mosquito larvicides. High rates of adsorption to dense particulate matter and toxin degradation in water may be expected to reduce Bti effectiveness. Therefore, water from wastewater lagoons may serve as a protective habitat for mosquito larvae against Bti larvicides relative to natural wetlands. We conducted a study in which we exposed larvae of Culex tarsalis to various concentrations of Bti in water collected from an urban wetlands and an urban wastewater pond. We used survival analysis and a comparison of life-history characteristics to assess the effects of aquatic media on the relative efficacy of Bti and on fitness indicators. In our study, mosquitoes reared in wastewater and exposed to high (100% of minimum field application rate) and medium (50% of minimum field application rate) concentrations of Bti experienced significantly higher mortality than mosquitoes exposed to corresponding concentrations but reared in water from natural urban wetlands. In addition, females that emerged from wastewater had shorter wings than those that emerged from wetland-collected water. These effects may have been due to higher turbidity and higher ionic concentrations in wastewater than water from natural wetlands.